Mars lander aims for touchdown in 'Green Valley'

The Phoenix spacecraft is en route to land in a spot called Green Valley near Mars’s north pole on 25 May (Illustration: NASA/JPL/Corby Waste)

With less than two months to go before it is due to land on Mars, NASA’s Phoenix probe has been directed towards a specific landing site called Green Valley. The site has few boulders that could potentially endanger a landing and lots of water ice for the lander to study.

Phoenix launched in August 2007 on a mission to Mars’s icy north polar region. The ice may have occasionally melted in the past due to changes in the Red Planet’s tilt, raising the tantalising possibility that microscopic life forms could once have eked out an existence there. Life might even be present there now in a dormant state.

The lander will dig down as much as 50 centimetres below the surface, collecting samples of soil and ice that it will examine to better understand the region’s past climate and check for complex molecules that could be associated with life. The lander is expected to operate for 90 days.

The north polar region has always been Phoenix’s general destination, but scientists have wanted to continue studying the region with other spacecraft before deciding where it should touch down. An engine burn on Thursday was the first intended to refine the spacecraft’s path for a specific landing site.

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Green zone

Green Valley has relatively few large rocks that could pose a threat to Phoenix when it lands. Its name derives from colour-coded maps used by mission planners that label the safest areas in green.

Another site that once looked promising, called Region B, turned out to be strewn with boulders in high-resolution images taken by the Mars Reconnaissance Orbiter (MRO), ruling it out as a landing site.

Mission planners are now aiming for an oval-shaped plot of land within Green Valley that measures 20 by 100 kilometres across.

NASA has given its tentative approval for Phoenix to land in this zone, but is reserving a final decision until later in April. That’s when MRO will obtain more images of a small spot at one end of the ellipse that has not yet been observed at high resolution.

If any hazards appear, there is still time to adjust the landing zone. “It’s not going to move by more than a kilometre or two,” Phoenix’s chief scientist Peter Smith of the University of Arizona in Tucson, US, told New Scientist.